This invention relates generally to improvements in tracking silicon wafers and, particularly, to a radio frequency identification system and method using a custom interface protocol for tracking silicon wafers through various stages of the wafer manufacturing process.
Most processes for fabricating semiconductor electronic components start with monocrystalline, or single crystal, silicon in the form of wafers. In general, semiconductor wafers are produced by thinly slicing a single crystal silicon ingot. After slicing, each wafer undergoes a number of processing operations to shape the wafer, reduce its thickness, remove damage caused by the slicing operation, and to create a highly reflective surface.
As an example, the manufacturing process includes rounding the peripheral edge of each wafer first, such as by an edge grinding operation, to reduce the risk of wafer damage during further processing. Next, a lapping process removes material from the front and back surface of each wafer to remove surface damage caused by the slicing operation and to make the opposing front and back surfaces of the wafer generally flat and parallel. The wafers are then etched by fully immersing each wafer in a chemical etchant to further reduce the thickness of the wafer and remove mechanical damage produced by the lapping and/or grinding operation. This produces a smooth surface on the wafer. Finally, the front surface of each wafer is polished, using a polishing pad and a polishing slurry made up of abrasive particles and a chemical etchant, to remove a small amount of material from the front surface of each wafer. The polishing operation removes damage induced by the etching operation and produces a highly reflective, damage-free surface on at least one face of each wafer. It is upon this polished face that integrated circuit fabrication takes place. In addition to various wafer shaping processes, wafers typically undergo a number of tests to measure their characteristics and quality before they are used in the manufacture of semiconductor electronic components.
Typically, the different steps of the wafer shaping and testing processes are performed at different locations within a semiconductor wafer manufacturing plant. For this reason, wafers must be transported facility-to-facility within the plant. A wafer carrier holds multiple wafers in position for transport between the different processing steps. Some processing steps occur with the wafers in the carrier while the wafers are removed from the carrier (and then returned) for other processing steps. For example, a wafer cassette formed with integral dividers defining slots, each of which receives a wafer, holds multiple wafers with minimal contact of the front and rear surfaces of the wafer. The wafers may be loaded into and unloaded from the cassette slots manually, or automatically by presently available machinery. Commonly assigned U.S. Pat. No. 5,592,295, the entire disclosure of which is incorporated herein by reference, discloses a wafer cassette of conventional construction for holding a plurality of semiconductor wafers.
For a number of reasons, including quality control, wafer manufacturers desire to track wafer lots as they travel facility-to-facility within a plant and to record process data on each lot cut from a particular ingot through final packing. In this respect, a single lot may comprise one or more cassettes and each cassette, loaded with wafers cut from a specific ingot, may travel independently of the other cassettes in the same lot.
Several devices are presently available for automatically identifying various objects, including bar-code reading and optical character recognition, for use in warehousing, distribution and manufacturing processes. Such identification devices visually identify distinctive markings on an object (e.g., a unique bar-code label) to identify it. Although these devices are useful in many applications, water, acids, and other substances associated with wafer processing are often destructive to the medium. Further, the ink used in the bar-codes can contaminate the wafers.
U.S. Pat. Nos. 4,827,110 and 4,888,473, the entire disclosures of which are incorporated herein by reference, describe systems for monitoring the progress of wafers through multiple processing operations using a transponder tag attached to the wafer carrier. In these patents, the transponder tags are coded to identify the carrier and a batch of wafers contained in the carrier. A remote recognition reader drives an associated antenna to propagate a radio frequency (RF) signal and the transponder tags identify the associated carrier in response to the RF signal. The systems disclosed in these patents, however, are controlled by mini-RF modules which cannot be custom programmed. In addition, the mini-RF module signal output requires the reader to be located in very close proximity to each antenna (i.e., read point). This is not acceptable in all applications within the relatively close quarters in semiconductor wafer process lines. Further, conventional identification devices lack several advanced functional parameters and cannot be upgraded to meet desired specifications.
For these reasons, a system is desired for tracking wafer lots which provides improved automatic identification, tracking and data collection as well as custom protocol interfaces with designated equipment.